In an electronic component which is configured in integrated form, it is customary for two conductive layers which are electrically insulated by a nonconductive layer to be electrically conductively connected to one another by a contact hole being etched through the nonconductive layer. The contact hole is filled with metal, resulting in the production of a metallic through-plating which electrically conductively connects the two conductive layers together.
One drawback of this procedure is that, in particular as the lateral dimensions decrease, i.e. as the diameter of a contact hole passing through the nonconductive layer decreases, and as the vertical extent increases, or at least as the aspect ratio increases, complete filling of the contact hole with metal is problematic and susceptible to defects. In particular, the deposited metal often blocks the upper region of the contact hole, preventing the whole of the contact hole from being filled with metal. Consequently, it is often impossible to produce an electrically conductive connection between the two conductive layers. Moreover, an incompletely filled contact hole leads to reliability problems.
A further drawback of the known procedure is that, in the case of a contact hole with a very low aspect ratio, the conductivity of the metallic through-plating drops considerably, i.e. the metallic through-plating constitutes an element which considerably limits the scaling of a metallization system and therefore of an integrated circuit, in which it is necessary for a plurality of conductive layers to be electrically conductively connected to one another through nonconductive layers in the vertical direction of an electronic component.
On account of the suitability of nanotubes, in particular carbon nanotubes, as metallic conductors and as semiconductors, in the context of nanotechnology it is desirable for nanotubes of this type to be integrated in electronic components.
By way of example, Jung Sang Suh and Jin Seung Lee, Highly Ordered Two-Dimensional Carbon Nanotubes Areas, Applied Physics Letters, Vol. 75, No. 14, pp. 2047-1049, October 1999, have disclosed a process for the self-aligned growth of carbon nanotubes in a perforated Al2O3 matrix.
Hitherto, nanotubes have only been arranged on the surface of metal contacts by means of a single catalyst layer (DE 100 06 964 C2). In this case, the catalyst and metal layers are normally applied by means of physical deposition (e.g. sputtering) to a flat substrate which has been patterned with resist, and these layers are then patterned using a lift-off process. However, there is at present no tried-and-tested process for vertical structures allowing a catalyst system to be positioned accurately at the bottom of these structures in order then for nanotubes, in particular single-walled carbon nanotubes (SWCNTs) or multi-walled carbon nanotubes (MWCNTs) to be synthesized or grown in the vertical structure with catalytically accelerated growth. Another process is the electrolytic deposition of a corresponding catalyst system for accelerating the growth of these nanotubes in vertical structures. In this case, however, it is difficult to monitor the quantity of catalyst metal which is deposited. Moreover, electrolytic deposition of very small quantities of a catalyst, as required for example for the synthesis of SWCNTs, is scarcely possible. Moreover, if the catalyst system is deposited physically in predefined vertical structures, it is not generally possible to prevent the catalyst also from being deposited on the side walls. Therefore, the nanotubes can also grow from the side walls. In this case, they are not in contact with the base of the vertical structure. A further process consists in applying the catalyst layer before the nonconductive layer and subsequently etching the vertical structures. However, process fluctuations and overetch mean that there has not hitherto been a solution for an accurate etching stop to the order of magnitude of approximately 1 nm. However, this is necessary in order to uncover a single catalyst layer for growth of the nanotube without, however, etching through this catalyst layer.